Full size radial tires have been built with highly elongatable cords in the belt plies for allowing the original unvulcanized tire to be built in a cylindrical shape, rather than the more conventional toroidal shape in which radial tires are normally built. Foldable spare tires of the bias-belted type have also been made; however, the same methods and constructions cannot be used to build a reduced diameter tire of the radial type because of the horrendous problems created by the radical difference between the cord angles of the reinforcement cords of the radial carcass plies and the cord angles of the cords in the belt structure. The invention is directed to the method of making and the construction of a stretchable radial tire which, when deflated, is as small as the foldable spare tires of the prior art.
Briefly stated, the invention is in a stretchable radial tire which is molded and vulcanized in a small, unstretched configuration and which is highly expansible upon inflation of the tire. This is made possible by the use, in the carcass plies and belt structure, of reinforcement cords which initially have a relatively high modulus of elasticity and then after vulcanization a relatively low modulus of elasticity up to a predetermined elongation when the cords develop a relatively high modulus of elasticity.